Page 31 - Chemical Process Equipment - Selection and Design

8 INTRODUCTION

TABLE 1.5. Some Potential Hazards TABLE 1.6. Safety Checklist of Questions About Chemical
Reactions
Energy Source
Process chemicals, fuels, nuclear reactors, generators, batteries 1. Define potentially hazardous reactions. How are they isolated?
Source of ignition, radio frequency energy sources, activators, Prevented? (See Chaps. 4, 5, and 16)
radiation sources 2. Define process variables which could, or do, approach limiting
Rotating machinery, prime movers, pulverisers, grinders, conveyors, conditions for hazard. What safeguards are provided against such
belts, cranes variables?
Pressure containers, moving objects, falling objects 3. What unwanted hazardous reactions can be developed through
unlikelyflow or process conditions or through contamination?
Release of Material 4. What combustible mixtures can occur within equipment?
Spillage, leakage, vented material 5. What precautions are taken for processes operating near or within
Exposure effects, toxicity, burns, bruises, biological effects the flammable limits? (Reference: S&PP Design Guide No. 8.) (See
Flammability, reactivity, explosiveness, corrosivity and fire-promoting Chap. 19)
properties of chemicals 6. What are process margins of safety for all reactants and
Wetted surfaces, reduced visibility, falls, noise, damage intermediates in the process?
Dust formation, mist formation, spray 7. List known reaction rate data on the normal and possible abnormal
reactions
Fire hazard 8. How much heat must be removed for normal, or abnormally
Fire, fire spread, fireballs, radiation possible, exothermic reactions? (see Chaps. 7, 17, and 18)
Explosion, secondary explosion, domino effects 9. How thoroughly is the chemistry of the process including desired
Noise, smoke, toxic fumes, exposure effects and undesired reactions known? (See NFPA 491 M, Manual of
Collapse, falling objects, fragmentation Hazardous Chemical Reactions)
IO. What provision is made for rapid disposal of reactants if required by
Process state emergency?
High/low/changing temperature and pressure 11. What provisions are made for handling impending runaways and
Stress concentrations, stress reversals, vibration, noise for short-stopping an existing runaway?
Structural damage or failure, falling objects, collapse 12. Discuss the hazardous reactions which could develop as a result of
Electrical shock and thermal effects, inadvertent activation, power mechanical equipment (pump, agitator, etc.) failure
source failure 13. Describe the hazardous process conditions that can result from
Radiation, internal fire, overheated vessel gradual or sudden blockage in equipment including lines
Failure of equipment/utility supply/flame/instrument/component 14. Review provisions for blockage removal or prevention
Start-up and shutdown condition 15. What raw materials or process materials or process conditions can
Maintenance, construction and inspection condition be adversely affected by extreme weather conditions? Protect
against such conditions
Environmental effects 16. Describe the process changes including plant operation that have
Effect of plant on surroundings, drainage, pollution, transport, wind been made since the previous process safety review
and light change, source of ignition/vibration/noise/radio
interference/fire spread/explosion (Fawcett and Wood, Safety and Accident Prevention in Chemical
Effect of surroundings on plant (as above) Operations, Wiley, New York, 1982, pp. 725-726. Chapter references
refer to this book.)
Climate, sun, wind, rain, snow, ice, grit, contaminants, humidity,
ambient conditions
Acts of God, earthquake, arson, flood, typhoon, force majeure
Site layout factors, groups of people, transport features, space
limitations, geology, geography TABLE 1.7. Safety Checklist of Questions About Start-up and
Shut-down
Processes
Processes subject to explosive reaction or detonation Start-up Mode (64.1)
Processes which react energetically with water or common D1 Can the start-uD of Dlant be exDedited safely? Check the following:
.
.
contaminants Abnormal concentrations, phases, temperatures, pressures,
Processes subject to spontaneous polymerisation or heating levels, flows, densities
Processes which are exothermic Abnormal quantities of raw materials, intermediates and
Processes containing flammables and operated at high pressure or utilities (supply, handling and availability)
high temperature or both Abnormal quantities and types of effluents and emissions
Processes containing flammables and operated under refrigeration (81.6.10)
Processes in which intrinsically unstable compounds are present Different states of catalyst, regeneration, activation
Processes operating in or near the explosive range of materials Instruments out of range, not in service or de-activated,
Processes involving highly toxic materials incorrect readings, spurious trips
Processes subject to a dust or mist explosion hazard Manual control, wrong routeing, sequencing errors, poor
Processes with a large inventory of stored pressure energy identification of valves and lines in occasional use, lock-outs,
human error, improper start-up of equipment (particularly
Operations prime movers)
The vaporisation and diffusion of flammable or toxic liquids or gases Isolation, purging
The dusting and dispersion of combustible or toxic solids Removal of air, undesired process material, chemicals used for
The spraying, misting or fogging of flammable combustible materials cleaning, inerts, water, oils, construction debris and ingress of
or strong oxidising agents and their mixing same
The separation of hazardous chemicals from inerts or diluents Recycle or disposal of off-specification process materials
The temperature and pressure increase of unstable liquids Means for ensuring construction/maintenance completed
Any plant item failure on initial demand and during operation in
(Wells, Safety in Process Plant Design, George Godwin, London,
1980). this mode
Lighting of flames, introduction of material, limitation of
heating rate